The Properties and Generation of the Principal Winds

All the air has its course around the Earth from East to West.

This can be explained by describing the entire structure of the universe.

The eastern winds are usually much drier and make the air clearer and more serene than the western winds.

This is because the western winds oppose the usual course of vapors. These trap those vapors and cause them to thicken into clouds. Whereas the eastern winds push them away and disperse them.

• The eastern winds blow mainly in the morning.
• The western winds blow in the evening

This is because the Sun S:

• shines on the half ABC of the Earth.
• casts noon towards B and midnight towards D
• sets for people in A
• rises for people in C

The vapors near B are greatly expanded by the heat of the day. They flow:

• partly towards A
• partly towards C
• partly towards D where they occupy the space left by those condensed by the coolness of the night.

Thus, they create a west wind towards A, where the sun sets, and an east wind towards C, where it rises.

The east wind is usually stronger and faster than the west wind because:

• it follows the course of the entire mass of air
• the Earth between C and D has more condensation of vapors because it has had no sunlight longer than D and A

The north winds blow mainly during the day. They come from high to low and are very violent, cold, and dry.

This is because Earth EBFD is covered with several clouds and fogs towards the poles E and F.

• There, it is hardly warmed by the sun.
• B is the equator where it shines directly, stirring up a quantity of vapors.

These vapors are strongly agitated by the action of its light.

• They rise very quickly until they are so elevated that the resistance of their weight prevents them from continuing straight upwards.
• Instead, it becomes easier for them to turn aside and go towards I and M above the clouds G and K

These clouds G and K are also heated and decompressed by the sun at the same time.

• They turn into vapors that flow from G to H and from K to L rather than towards E and F.

This is because the dense air towards the poles resists them.

• On the contrary, the vapors rising from B are very agitated and are ready to move in all directions
• They can easily give way.

The North and South Winds

F is the Arctic Pole. The course of these vapors from K towards L creates a north wind, which blows during the day in Europe.

This wind blows downwards because it comes from the clouds towards the earth.

• It is usually very strong because it is stirred by the strongest midday heat

• This wind is very cold and very dry, partly because of its strength, since impetuous winds are always dry and cold
• It is dry because it is usually composed only of the coarser parts of fresh water mixed with air, whereas humidity mainly depends on the finer parts.

These are hardly found in the clouds from which it originates because they partake much more of the nature of ice than of water.

It is cold because it brings with it towards the south the very subtle matter that was towards the north, on which primarily the coldness depends.

On the contrary, the southern winds blow more often during the night, coming from below upwards, and are gentle and humid.

This is because part D is in nighttime. It still retains enough heat that the sun has given it during the day to release several vapors.

• But the air above towards P does not retain as much in proportion.

Generally:

• coarse and heavy bodies always retain their heat longer than those that are light and subtle.
• hard bodies also retain it longer than those that are liquid.

This is why the vapors found towards P stop and thicken into clouds.

• They do not continue their course towards Q and R
• This cloud prevents those coming from the earth D from rising higher, forcing them towards N and O
• This creates a southern wind which blows mainly during the night and comes from the earth upwards towards the air.

This southern wind is very slow because:

• its course is delayed by the density of the night air
• its material comes only from the earth or water and not the clouds
  • It cannot expand so rapidly or in such quantity as that of other winds, which usually come from clouds.

It is warm and humid, partly because of the slowness of its course.

• It is humid because it is made up of both the finest and coarsest parts of fresh water
• It is warm because it brings with it towards the north the subtle matter that was towards the south.

Springtime

In March, and generally throughout spring:

• the winds are drier
• the changes of weather more sudden and frequent, than in any other season of the year.

This is because the sun 3 months earlier at autumn was around circle HN, representing the Tropic of Capricorn.

• It heated BFD much less and BED more
• But now at spring, it does the reverse

Consequently, this half BFD was much more covered with snow.

• All the air surrounding it is much denser and filled with more clouds than the air surrounding BED.

This causes:

• much more vapor to expand at BFD during the day
• much more to condense during the night, conversely

Now, the earth at BED is less heated and the force of the sun there is not less.

• This creates more inequality between the day’s heat and the night’s cold.
• These eastern winds blow mainly in the morning.
• Those from the north blow around midday
• Both winds are very dry

At springtime, they must there be much stronger and more abundant than in any other season.

The western winds blow in the evening are are also quite strong there. This is for the same reason as the eastern ones that blow in the morning.

They encounter each other and generate rains or storms. These usually cease soon after because the eastern and northern winds, which drive away the clouds, remain dominant.

Ornithies

The Greeks called these eastern and northern winds as Ornithies, because they bring back the birds that come in spring.

They observed the Etesians after the summer solstice. They come from the vapors that the sun raises from the lands and waters of the North, after having already spent quite a long time towards the Tropic of Cancer.

It lingers much more proportionally towards the Tropics than it does in the space between the two.

During March, April, and May, it dissolves into vapors and winds most of the clouds and snows that are towards our Pole.

But it cannot heat the lands and waters enough there to raise other vapors that cause winds until a few weeks later, when this great day of six months, which it has there, is a little beyond its midday.